1. Field of the Invention:
This invention relates to a windshield wiper control system, more particularly to a control system containing solid state motor driving and braking control along with associated short circuit and transient protection for a plurality of modes of operation of the windshield wipers.
2. Prior Art:
In turning on the windshield wiper motor, various reference voltages throughout the controller system are disturbed. The disturbance often causes the input voltage to the motor drivers to oscillate causing erratic motor operations. If a short circuit protection circuit connects in the path of the motor current, generally this circuit also will act erratic and respond in a manner that inhibits motor operation.
U.S. Pat. No. 4,705,997 of D. L. Juzswik dated Nov. 10, 1987 entitled "Bidirectional Motor Drive Circuit" teaches a motor drive circuit that may include transient protection circuits, but the protection circuit operates to prevent voltage transients greater than a predetermined amplitude from being passed to the drive circuitry; i.e., at least the high-side power FETS are selected to have a minimum breakdown voltage which is at least twice the amplitude of the transient protection. Such an arrangement appears to provide adequate protection but it requires sizing FET parameters to anticipate transient voltages.
Another control circuit is described in U.S. Pat. No. 4,825,134 dated Apr. 25, 1989 of Tracht entitled "Intermittent Wiper Control Circuit With Instant Wipe". In this patent, a voltage comparison arrangement provides a first wipe capability for an intermittent wipe cycle. The comparators employed provide control signals to operate relays used to activate the wiper motor. The comparator arrangement doesn't appear to place limitations on the design of the wiper circuit but it does appear to lack transient combating circuits which oppose transients caused by the switching ON and OFF and reversing direction of motor currents.
Realizing the various problems associated with switching OFF and ON signals to induction-type motors, a search for various means to provide a plurality of controls for controlling the operation of the wiper motor and at the same time guarantee snap-action switching of the various controls with protection from transients and short circuits. This search resulted in the improved windshield wash and wipe controller of the present invention.